If you are getting the message about needing a Session ID, then it means that you are clicking on the MAGIX Screenshare icon.
This is a supplementary piece of software that can be used for remotely viewing other user's screens.
The version that comes free with MAGIX software, only allows you to accept incoming sessions. This is why it asks for the ID, only the Deluxe version allows you to create your own session.
In all cases, please make sure that you are clicking on the actual icon for your software and not the MAGIX Screensharing icon.
The software can be removed through the Control Panel. It is harmless and will only allow other people to view your screen if you are running the software and enter in their session ID.